A migration expert warns that there are more than 50 million Muslims willing to accept violence and support those who carry out terror attacks to defend their religion.

Professor Ruud Koopmans of the Netherlands warned the EU on Monday to block the entry of any refugees whose identity cannot be categorically confirmed.

Koopmans said that of the 1billion adult Muslims in the world, ‘half of them are attached to an arch-conservative Islam which places little worth on the rights of women, homosexuals, and people of other faiths’.

In an interview with a German news website he claimed that of these 500 million conservative Muslims, at least – and probably more – than 50 million are willing to sanction violence.

Koopmans, who is a professor of sociology and migration research at the Humboldt University of Berlin and the director of integration research at the WZB Berlin Social Science Centre, stressed that not every one of them was ready to exert violence directly.

But he added: ‘They support the radicals, they encourage them and provide them shelter or simply keep their mouths shut when they observe radicalization.’

He says he considers his own estimate of 50 million ‘an understatement’, citing studies that show eight per cent of German Muslims agreed to the use of violence against ‘Infidels,’ while in his own country 11 per cent of Muslims agreed with the statement: ‘There are situations in which it is acceptable for me from the perspective of my religion, that I use violence’.

In several Islamic countries, 14 per cent of local Muslims think suicide attacks against innocents are ‘sometimes’ or ‘often’ justified to defend Islam, said Koopmans, citing a study by the US-based Pew Research Center.